The present invention relates to a variable-valve-actuation (VVA) apparatus for an internal combustion engine that can vary, particularly, the lift amount of valves such as an intake valve and exhaust valve in accordance with engine operating conditions.
As disclosed in U.S. Pat. No. 6,029,618 issued Feb. 29, 2000 to Hara et al., the VVA apparatus typically comprises a crank cam arranged at the outer periphery of a driving shaft that rotates in synchronism with a crankshaft and having an axis eccentric to an axis of the driving shaft, and a valve operating (VO) cam to which torque of the crank cam is transmitted through a transmission mechanism to have a cam face coming in slide contact with the top face of a valve lifter arranged at the upper end of an intake valve for opening and closing operation thereof.
The transmission mechanism includes a rocker arm disposed above the VO cam and swingably supported to a control shaft, a crank arm having an annular base engaged with the outer peripheral surface of the crank cam and an extension rotatably connected to a first arm of the rocker arm through a pin, and a link rod having a first end rotatably connected to a second arm of the rocker arm through a pin and a second end rotatably connected to an end of the VO cam through a pin.
Moreover, fixed on the outer peripheral surface of the control shaft is a control cam having an axis eccentric to an axis of the control shaft by a predetermined amount and rotatably fitted in a support hole formed substantially in the center of the rocker arm. The control cam changes a rocking fulcrum of the rocker arm in accordance with the rotated position to change the position of contact of the cam face of the VO cam with respect to the top face of the valve lifter, carrying out variable control of the lift amount of the intake valve.
Specifically, when the engine operating conditions are in the low-rotation and low-load range, for example, in order to urge an actuator to rotate the control shaft clockwise, for example, for rotation of the control cam in the same direction, the rocking fulcrum of the rocker arm is moved to a certain position. Then, pivotal points of the rocker arm with the crank arm and link rod are moved leftward to draw up an end or cam nose of the VO cam, moving the position of contact of the VO cam with respect to the top face of the valve lifter to a base portion of the VO cam. Thus, the intake valve is controlled to have zero lift in the valve-lift characteristic, achieving the valve-stop state so called.
On the other hand, when the engine operating conditions are in the high-rotation and high-load range, the actuator rotates the control cam counterclockwise from the certain position through the control shaft, moving the rocking fulcrum of the rocker arm downward. Then, the cam nose of the VO cam is pushed downward by the link rod, etc. to move the position of contact of the VO cam with respect to the top face of the valve lifter to a lift top portion of the VO cam. Thus, the intake valve is controlled to have greater lift in the valve-lift characteristic.
Therefore, outstanding engine performance can be obtained, e.g. improvement in fuel consumption by valve stop in the engine low-rotation and low-load range and increase in engine output, etc. by improved intake-air charging efficiency in the engine high-rotation and high-load range. It is noted that an improvement in fuel consumption by valve stop is achieved by stopping actuation of the intake and exhaust valves of particular cylinders, i.e. carrying out reduced cylinder operation so called, or actuation of one of the two intake valves to produce swirl in a combustion chamber.
However, the VVA apparatus generally have dimensional errors of components produced upon manufacture thereof, which are naturally included in the respective cylinders to which the apparatus are mounted and have different magnitudes. The lift amount of the valves variably controlled by the VVA apparatus is not seriously affected by a dimensional error of the components in the region of medium lift to high lift since the engine can be in high rotation therein. It is, however, greatly affected by a dimensional error of the components in the region of low lift, particularly, very low lift since the engine can be in low rotation therein, where engine rotation is apt to vary.
Moreover, variation in the machining accuracy of components of the VVA apparatus results in variation in the lift amount of the valves, which are the greatest in the region of very low lift with respect to in the region of medium lift to high lift. Thus, during engine operation in the very low lift area, the mixture charging efficiency and gas flow conditions in the combustion chamber may be apt to vary between the cylinders, resulting in unstable engine rotation and lowered engine performance.
This causes need of enhanced machining accuracy of the components of the VVA apparatus, raising an inevitable technical challenge of increased manufacturing cost.
It is, therefore, an object of the present invention to provide a VVA apparatus for an internal combustion engine, which contributes to an improvement in the engine performance without any increase in manufacturing cost.
The present invention provides generally a variable-valve-actuation (VVA) apparatus for an internal combustion engine with valves, comprising:
an operating mechanism that changes a lift amount of the valves; and
a microcomputer-based controller that controls said operating mechanism to change said lift amount in accordance with operating conditions of the engine, a first portion of said lift amount between a predetermined high value and a predetermined low value being changed continuously, a second portion of said lift amount between said predetermined low value and zero being changed with one of said predetermined low value and zero selected.
One aspect of the present invention is to provide a variable-valve-actuation (VVA) apparatus for an internal combustion engine with valves, comprising:
an operating mechanism that changes a lift amount of the valves, said operating mechanism comprising a driving shaft rotated by a crankshaft of the engine and provided with a crank cam at a outer periphery thereof, a valve operating (VO) cam coming in slide contact with a top face of a valve lifter disposed at an upper end of each valve to open and close it, a transmission mechanism connected between said crank cam and said VO cam, and an alteration mechanism for variably controlling an operation position of said transmission mechanism to change a position of contact of said VO cam with respect to said top face of said valve lifter; and
a microcomputer-based controller that controls said operating mechanism to change said lift amount in accordance with operating conditions of the engine, a first portion of said lift amount between a predetermined high value and a predetermined low value being changed continuously, a second portion of said lift amount between said predetermined low value and zero being changed with one of said predetermined low value and zero selected.
The other objects and features of the present invention will become understood from the following description with reference to the accompanying drawings.